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Why do we seldom see small unmanned aircraft with gasoline engines?
Most commercially available FLYING WINGS (RC aircraft or UAVs) are battery powered. Why aren't there more with with gasoline engines?
PS: Sorry I edited. The question is specific about flying wings configuration.

I assume you are talking about two stroke RC engines and not 4 stroke ones?

Why the downvotes?

@qqjkztd I never meant to imply that there weren't 4 stroke RC engines... I was getting at general glow-type engines for lower-end RC aircraft versus higher end stuff.

If you're talking small drones, they often carry cameras. If you've ever held a gas-powered RC aircraft while the engine's running, you'll notice quite a bit of vibration. Vibration + Video = Useless Video. Image stabilization won't help much, if at all, with the constant buzz of a small RC engine.

Sorry i should clarify the question. my question is specific about FLYING WINGS configuration.

Because electric is the best propulsion method available for small commercial UAVs and their mission profiles:
-Significantly quieter
-No smells involved
-No flammable liquid involved
-Way easier to operate: properly tuning an RC gas engine is not for everybody
-Much lower vibration and on frequencies easier to filter out
-More controllability, a BLDC (brushless DC) motor has near-instant response to the throttle and thus enables the actual, simple building scheme of quadcopters

Big UAV's (like military/intelligence ones) are usually powered by turbines, so jet fuel.

@SnakeDoc even the ones with a propeller?

@Baldrickk Propelled-powered military UAVs designed for long range missions (i.e. not the ones to "take a look behind the hill") use gas engines, often with ultralight sportplanes origins.

@Baldrickk Yes, called a turbo-prop. The turbine powers the propeller, instead of pistons. Take a look: https://en.wikipedia.org/wiki/General_Atomics_MQ-9_Reaper#Specifications and here's the turbine: https://en.wikipedia.org/wiki/Garrett_TPE331

To sum it up: large (up to now mainly military) drones have mission profiles very similar to the "manned crafts we are used to" so the propulsion systems are basically the same, with electric still playing a marginal role

Not so long ago, internal combustion engines were the standard for R/C aircraft. They had some big drawbacks though:

these engines used nitromethane fuel, which is a solvent that attacks many common materials used in RC aircraft, and leaves everything covered in a smelly film
they are loud and run at high temperatures
they need to be fiddled with to get them to run well
if you have multiple engines, you have the extra problem of having to match their power output

When electric motors + battery packs reached the point where their power/weight ratio was high enough for use in RC aircraft, many hobbyists switched to this (more convenient) option.
For larger aircraft, the square/cube law means higher demands on power/weight ratio, and electric systems still lag behind gas engines in this regard. So large UAVs will have internal combustion engines.
A large variety of R/C engines is still available, from single-cylinder two-stroke glowplug engines with less than 1 cm3 displacement, to 4-strokes, multi-cylinder engines, mini turbines, up to a 1/4 scale Rolls Royce Merlin.

Thank you. the question is specific about flying wings. i highlited in the question.

Many UAVs do used internal combustion 2 or 4 stroke engines. Examples include the Scan Eagle, Integrator and RQ-21 Blackjack from Insitu/Boeing. The Scan Eagle has demonstrated flight of 29 hours nonstop. Electric motors are limited by their battery weight and size; internal combustion fuel has far more energy per unit weight or volume.
Of course, these have weights of 30 to 140 pounds (15 to 60 kg) and only need one motor each. For quadrotors and such, the complexity of getting the engine rotation to the multiple rotors and controlling same isn't worth the trouble for most realistic designs.

Thank you. the question is specific about flying wings. i highlited in the question

Much depends on the configuration. Flying wings generally have less yaw stability than conventional layouts with a larger moment arm to the vertical stabilizer and rudder. So if more than one engine is used, they need to be thrust balanced closely. That's more difficult to do well with internal combustion engines while servoing the power to electric motors is relatively trivial to ensure synchronization. Combined with the above mentioned quietness, ease of use, lack of oil spray and mess, exhaust noise and so on, the performance of modern battery powered motors makes them much more appealing.

these are common problem to all fixed wing configurations. not specific to flying wings.

The Scan Eagle (Insitu X-200) is a tailless aircraft, i.e. a flying wing with a cylindrical payload/body with all control surfaces on the wing and winglets. Is that close enough? And with a single engine, the synchronization mentioned doesn't arise. There are a number of flying wing UAVs with gasoline engines from other manufacturers as well, though the ScanEagle configuration allows low drag incorporation of a stabilized camera system on the nose, among other advantages.


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Can the mass flow rate for different power settings be determined?
Is it possible to determine the mass flow rate for different power settings? Unfortunately I was unsuccessful in finding the engine specification for the PW2037 so I used the data from this source, which states that the mass flow rate at take-off for the PW2037 engine is 1210 lb/s. Given this flow rate, would it be possible to calculate the mass flow rate at idle setting? And therefore also the mass flow rate for 50% engine setting (or 25%, 75%, etc.)?
An answer in this question suggests using thermodynamic equations to approach this. However, I am not too sure on how to use these equations.

Prediction of the mass flow, fuel flow and thrust can be given without detailed knowledge of the compressor and turbine maps, as the pdf in this link states, when we assume that the LP turbine is always choked because it operates in front of an exhaust nozzle.
The linked pdf gives an elaborate method for determining the off-design parameters for different turbofan engine configurations. The difficulty is that all parameters change relative to each other: mass flow, thrust, fuel flow, even the bypass ratio.
The paper matches the computed data with actual published data of two turbofan engines, neither of which unfortunately are from the PW2000 series. The closest one calculated is the RB211, which is a three-spool design but the twin spool simulation calculation works for the 3-spool as well according to the article:

The added assumption that the LP turbine is choked, makes the three-spool case exactly similar to a twin- spool engine. The design point calculations are nearly the same as those for the twin spool. So one can effectively use the same program for three-spool and twin- spool engines, with the only difference that the inter- turbine and inter-compressor temperatures and pressures calculated will be totally different from the actual values.

Meaning that the model will create good results for the overall parameters even though some of the internal parameters won't match. Figure 7. then gives the mass flow as a function of hot and cold thrust for the RB211 engine:

Thrust----Mass Flow
100 % --- 100 %
75 % --------87%
50 % --------71%
25 % --------51%
8 % ---------30 % (idle)

So without going through the detailed procedures for the OP specific engine, above gives data for a comparable engine class.

I noticed this assumes an aircraft flying at 30,000 ft at Mach 0.80. Would these values be any different than say at rest at sea level? So would an engine at rest at sea level have a mass flow of 30%?

@Zack hard to tell without doing the actual calculations in the paper. Have seen a graph somewhere that seems to indicate an idle thrust flow of about 30% but cannot find it anymore. Sorry, am lacking the time to be of more help at the moment.

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How is the jet engine inlet danger area affected when airborne?
Boeing published engine hazard areas as shown below:

I am curious as to how the danger area is affected when the aircraft is in flight as the jet engine is still vulnerable to foreign object damage.

Assuming idle power conditions at 10000 ft (or just airborne in general), are the danger zones the same as on the ground? If not, would there be a way to calculate this?
Knowing the danger zone for both idle and full power, would it be possible to calculate the danger zone distance for different power settings? E.g. 50% N1.

It is doubtful that the area in front of the engines is significant given that the aircraft will probably be outrunning the inlet stream. The area behind the engines will probably combine with the wake of the aircraft, and would probably be difficult to separate the two (or at least not useful since the combined effect is what somebody following the aircraft would be concerned about). If you are asking if something ahead of the aircraft but not directly in the intake stream can get ingested, the answer, I'm guessing, is probably not.

The "danger zones" that you reference only have meaning when the aircraft is on the ground.  Once you're flying, everything in front of the aircraft is in danger of being either sucked into an engine, or else struck by some part of the aircraft structure. How far in front of the aircraft you'd define this "danger zone" would be based as much on assumed reaction time (to get out of the way of a 200? 300? 400? knot aircraft) as on anything else.  You can't extrapolate the posted figures into anything comparable for "in flight" conditions -- the dangers (to skydivers?) just aren't the same!

@RonBeyer I'm guessing this would depend on the weight of the object being ingested as well? E.g. a small, light RC plane not positioned directly in the intake stream could still be sucked in if close enough to the engine?

I think you should precise what you understanding of "danger area". It is primary defined for airport workers on the ground, but as you speak of suction area, you may define what you understand by being in or out of this area.

Might.  Provided there was anything at 10,000 ft to accidentally ingest other than air.

@CarloFelicione Bird strikes have been reported at altitudes above 30,000 feet.

Let's assume the A320 is powered by V2500 engines, one of the options for it. This engine has an air mass flow of 355 kg/s. At sea level, air density is 1.225kg per cubic m. Hence, 355 kg/s = 355/1.225 = 290 cubic m/s.
Now, let's assume the aircraft is still at sea level, but now at Mach 0.8 (unrealistic, but we'll correct that next). The fan diameter is 1.6 m, which gives an intake area of 2.0 sq.m. Also, Mn 0.8 at 0ft is 272m/s. Hence, every second, the intake sweeps a volume of 272 x 2.0 = 544 cubic m. But, the engine only needs 290 cubic/m of air, per second assuming air density in the intake is the same as the air surrounding the aircraft. Therefore, the diameter of a streamline tube of the intake air will actually be smaller than the diameter of the engine inlet. It will be the area that sweeps 290 cubic m/s at 272m/s = 290/272 = 1.07 sq. m., or a diameter of 1.17m, not 1.6m.
Basically, the engine takes the airflow it wants, not what the intake area x forward speed provides. If the engine wants more (such as when the aircraft speed is low, or stationary, but the engine rpm is high, such as at the start of the takeoff roll), the engine will draw air from a large area in front of the engine (as per the max takeoff conditions diagram). Conversely, when the aircraft is at high speed, and the engine throttled back, the intake will spill the excess air it is providing (causing spillage drag).

Now, let's correct the fact the aircraft can't do Mn 0.8 at sea level. Let's re do the calculation at 35,000ft (10,700m). Here, air density is 0.38 kg per cubic m, and pressure and temperature are 3.46 psi and  219 Kelvin (-54C), compared with 14.7psi and 288 Kelvin (15C) at sea level. Thus our 355 kg/s, which is actually a corrected airflow, is a physical (real) air flow of 95.8 kg/s at 35,000ft since theta = 219/288 = 0.76 and delta = 3.46/14.7 = 0.235. Now 95.8 kg/s at 0.38 kg/ cubic m = 252 cubic m per second. Also, Mn 0.8 at 35,000ft is now 237m/s, not 272 as it was at seal level. Hence, every seond the intake area of 2 sq.m is sweeping through 2 x 237 = 474 cubic m per second. But we only want it to sweep 252, hence we need to find the diameter of a streamline tube that will cause this, at 237m/s. Therefore, we need an area of 252/237 = 1.06 sq. m., which occurs with a diameter of 1.16m. This compares with the physical inlet diameter of 1.6m.
Thus, at Mn 0.8, 35,000ft, max power, the green area at the engine intake is now a tube, of 1.16m dia, that extends in front of the aircraft. For how far this extends, depends as suggested, on what reaction time is required for the aircraft to manoeuvre away from an obstacle in this region, or for the object (a bird?) to manoeuvre out of the aircraft's way.
The exact figure of 1.16 is questionable, as the assumption of air density in the intake not changing from the surrounding air is not entirely realistic. But the general result, is I believe, reasonable.

Should the diameter of the streamline tube at sea level not be 1.17m as opposed to 1.47m? (290/272 = 1.07 sq. m., diameter = 2 * √(1.07/3.14) )

Would it be correct in saying that if the engine intake diameter is less than the fan diameter (I.e. 1.6m) then the result would be a streamline tube extending in front of the aircraft? And, in the case that the engine intake diameter exceeds the fan diameter (1.6m), then the engine would draw air from a large area like in the diagrams?

Yes, I made a mistake with calculating the diameter from the area. It is a dia of 1.17m, as you say. I have corrected the answer - thanks.

With regard to your second comment, yes, I would agree in general with what you say.  Note in the first case, the engine doesn't have to suck, so it's not drawing the air in, just swallowing a portion of what the intake provides. In the second case, rather the engine taking air from a cylinder or tube in front of it, it would probably be drawing it from a shape more like a cone or a hemisphere, I expect. Sorry I missed your comments till now. The only odd thing with my answer, is that even in the extreme sea lavel case, the intake seems way oversized.

This makes sense. However, could the forward distance of this cone/hemisphere be calculated? For example, if the diameter of the cone/hemisphere is 1.1 metres, would the cone/hemisphere also be extending 1.1 metres forward?

@Zack. I'm not entirely sure I understand your question, but hopefully this comment does answer it. If the intake is drawing air from a cone or hemisphere that is 1.1 m dia, at the lip of the intake, how far this area extends forward of the intake depends on how you define the boundary between the air in it, and the surrounding air. If you define the boundary as the air that will enter the intake, compared to an adjacent air particle which will just miss, the area extends forwards forever, if the plane is in forward flight.

@Zack. If the plane is stationary, you need to define an air velocity which seperates the ambient air from the air entering the engine, as done in the diagrams in the picture of the question.

I apologise for the lack of clarity. I understand that the area will extend forever and any objects within that area will eventually be ingested by the engine (regardless of whether the engine force is currently acting upon it or not). However, I wanted to see if it was possible to calculate the area where the object would have the engine force acting upon it (the same way that such an area was defined in the original post).

So for an aircraft currently drawing air from beyond the engine (so air intake diameter is bigger than the engine inlet diameter), this area would be of a semi circular shape (like in the original post) and its area can be outlined by the diameter of the air intake - resulting in a shape similar to that in the original post. However, I am struggling to think how this same logic to calculate the area can be applied when the air intake diameter is less than the engine diameter and therefore results in a cone/hemisphere like shape.

@Zack.  Ok, let's explain it this way. The air enters the engine fan at about Mach 0.4. So, if the aircraft is slower than that, it's sucking air in. The area it's sucking from starts of being as large as in the diagram, and shaped like a hemisphere.  But as the speed increase, the air the engine wants is now starting to be provided by the forward motion, so the engine only has to draw air in from a smaller hemisphere. So, as the plane accelerates from stationary, the hemisphere shrinks. Once the plane reaches Mach 0.4, it basically just swallows the air that sits in front of the engine.

@Zack. So, the area of air the engine is acting upon is basically zero. Now, as the plane increases speed further, the air is effectively decelerating into the intake, not accelerating any more. Now the forward speed is providing more air than the engine wants, the diameter of the cylinder of air in front of the engine which is being swallowed reduces in diameter. The inlet is spilling air, and the engine is actually pushing some air away, or out of the intake. The air slows down as it enters the intake, and there is a ram air pressure rise in the intake. Hope that helps.

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Where could I find a MATLAB implementation of TCAS algorithms?
Where could I find a MATLAB implementation of TCAS algorithms and simulation?
My research work deals with collision avoidance of a multi-UAV scenario in a small airspace.

I'm not sure one exists, as Matlab is more towards mathematical analysis. I could see some kind of simulation in Simulink or Labview for doing hardware tests or software proving, but not Matlab.

The only organization I know that has a simulation for the TCAS logic is MITRE CAASD. They did the validation of the logic for the FAA. You may want to research TCAS X which is a new algorithm based version that's in development (and is intended to support UAVs.)

As mentioned by Gerry, MITRE has similation software for TCAS. Eurocontrol has simulation software as well, but I believe it uses the same simulation core. At the moment Eurocontrol is acquiring/developing a new TCAS/ACAS simulation tool, which should be interoperable with Matlab.

I am mainly looking for the algorithm so that I can understand it and implement something similar in MATLAB. I couldn't find the exact algorithm anywhere.

EGR115 Final Project, eh?

@SMSvonderTann Not really! I am trying to analyze UAV behavior as part of my Master's thesis.

@Sanchises A paid-for Matlab license exists many many schools, if not the student edition is <$100.

@Sanchises It is indeed an academic research project, so I don't have to worry about MATLAB license.

MIT LL did indeed build a TCAS model in Simulink/Matlab which was used to validate the algorithms. I doubt they will release it, but it's worth trying to start there.
Otherwise, they did release quite a bit of details in reports. You'll probably end up rebuilding it from their logic.

I will go through the reports that you shared. I just needed a pseudo code for TCAS logic at least to begin with.

I would try contacting the authors. They may be willing to share. Worst they'll just say no.

Right! I am gonna try contacting the authors.

If you are planning to build your own implementation and you are looking for the pseudo code of TCAS then buy a copy of the TCAS II MOPS. It includes the algorithm description.
You can find it as RTCA document DO-185B, Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance Systems II (TCAS II).

It's very expensive! I will try to find the logic somewhere online.

I don't think it is that expensive, your university should be able to afford it. Anyway, I think that TCAS II is not very well suited for a multi uav scenario in a small airspace. It will require quite some tweaking to get it to work. Perhaps it is better to brew your own CAS from looking at concepts used in TCAS. Perhaps this answer helps.

The answer certainly helps!

If the size of the airspace is small and you're just looking for collision avoidance between UAV's you'd probably be better off using FLARM, which is used by gliders. There is a variant of it called "UAS Electronic ID". The standard is open and available on request.


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What is the geoid undulation used for in aviation?
In addition of the altitude found on aerodrome information, the French AIP also mentions the value of the geoid undulation::

AIP for Lyon - Saint Exupéry (LFLL)
Geoid undulation is also found in Belgium, Switzerland, Poland, Morocco, Qatar, Sweden... AIP to name the ones that appear on the first pages of Google results.
US FAA on its side mentions the ellipsoidal height directly.
On the figure below:

Ellipsoidal height is $h$,
Geoid undulation is $N$
Orthometric height is $H$

Source
A GNSS receiver determines the ellipsoidal height $h$, and can display the orthometric height $H$ by adding/subtracting $N$ from grid values embedded in the device.

Is there any use of $N$ in aviation? In the cockpit?
Are the values of altitudes found on aviation charts equal to $h$ or to $H$ or something else? Does 821 ft expresses $H$ or $h$ for this aerodrome?

Note: As visible on the figure, the vertical direction determined by using $H$ is different than the one determined by using $h$, and if an aircraft is 35,000 ft above the ARP of Saint Exupéry, this gives two possible horizontal positions, which for aircraft can be very distant.

The question title asks about "use in aviation," but as edited the question seems to be asking more about "use in surveying".  Aviation, once you get to the point that an aircraft is involved, uses baro altitude and not much else -- meaning, no, what you're asking about isn't used "in aviation".  Used in the mapping & surveying that goes into the products aviators use, absolutely yes, but in the cockpit, we want to know "what's the field elevation" and there is one answer to that, a published number, which is also read on the altimeter. We care not about geoid or spheroid or etc.

@RalphJ: I asked why the geoid undulation is found in the AIP, but if you want to migrate it to another stack, I'm not against it, provided they can answer this question.

I'm not overly concerned about any need to migrate the question; all I'd say is that the geoid undulation number in the French AIP is a parameter that I've never encountered in US documents, neither in airline nor military operations. Somebody out there may use it, but I suspect it's much more used in the surveying/mapping realm than in any aviation operational capacity. Maybe it's just easier to publish that value in the AIP than in its own separate document.

I think gis.SE is the better place to ask. Anyway: usually the WGS84 (the original revision) is used as standard GPS reference. GPS altitude will (usually) give just this. Then other global models (updated more often) give the geoid (and possible referencing newer WGS84 revisions). I'm not sure if FR use one of such model, or a own measures (std global model are also not so precise). It give you just the difference about GPS altitude and "real" altitude (which is also not very well defined).

@BaileyS: "The geoid has more to do with mapping coordinates [...] than with actual altitude"... not sure I follow you. "Geoid: Specific equipotential (level) surface, which defines best, in a least-square sense, the global mean sea level. It is the true zero surface to measure elevations." (source)

@BaileyS: Not disagreeing with your latest comment. Current elevations are measured by optical leveling, in France the NGF. However it is expected, rather sooner than later, that elevations will be measured by satellites and the global geoid, which is an iso-gravity surface, will indeed be the reference replacing the tide gauges and other fundamental points. So saying the geoid is more related to horizontal mapping than for elevation reference is a bit surprising.

Short answer

Geoid undulation publication is a recommendation from ICAO. Not all countries are ready for it, and therefore the information is often missing. GNSS are sensors able to deliver the height above ellipsoid, to get the MSL value, one need to subtract the geoid undulation (some GNSS do this operation themselves, some not).

Undulation is not used by crews, and regulation prohibits the use of GNSS altitudes. For ATC officers and aircraft crews, enroute and terminal vertical navigation is done exclusively with barometric values, even when GNSS is used by the avionics in the background (like in LPV/GBS approaches).

Therefore at the moment, altitudes in charts are all expressed as above sea level (MSL) values, the common altitude reference.

Designing an approach with a GNSS vertical guidance requires knowing the geoid undulation as the procedure starts from MSL altitudes, but the final point (threshold crossing) of the procedure is encoded in the navigation database using ellipsoidal heights. Example, for a GBAAS approach the points LTP, GPIP and FPAP are not referenced to MSL, but to the ellipsoid (which differ from MSL by the geoid undulation):

GBAAS (GLS) approach design with LTP, GPIP and FPAP referenced to ellipsoidal height h. Source

It may take a long time before some countries are able to publish the undulation value for runways, as determining the undulation at the point of interest with a precision of 25 cm requires an extended leveling system, based on detailed gravimetric data from surveys connected to WGS-84 altitude reference points.

Undulation value is recommended by ICAO
WGS-84 Manual / Doc 9674:

1.4.8: GNSS-derived heights are referenced to the WGS-84 ellipsoid which will usually differ from the “normal” (orthometric) height at
the same point. The difference will be of significance in the
aerodrome environment when navigating with GNSS sensors. The
difference between orthometric height (geoid height, elevation) and
WGS-84 ellipsoidal height must therefore be made available to the
aviation community. The height that separates geoid and WGS-84
ellipsoid is the geoid undulation.
1.4.9: Geoid undulation is required for airport elevations, runway thresholds and touchdown and lift-off areas (TLOFs) or thresholds of
final approach and take-off areas (FATOs) at heliports. (See also
Appendix B.)

This recommendation is therefore also found in Annex 4 (Aeronautical Charts) of the Chicago Convention:

2.18.2.1 Mean sea level (MSL) datum, which gives the relationship of gravity-related height (elevation) to a surface known as the geoid,
shall be used as the vertical reference system.
2.18.2.2 In addition to the elevations referenced to MSL, for the specific surveyed ground positions, geoid undulation (referenced to
the WGS-84 ellipsoid) for those positions shall also be published as
specified for a particular chart.

and in Annex 15 (Aeronautical Information Services) which also recommends to determine the geoid undulation from the EGM96 gravimetric model, and when not used, to include proper transforms from the model used to EGM96.
ICAO related recommendations are not yet implemented everywhere
This doesn't mean all ICAO members currently implement these recommendations, e.g. in UK, from AIP GEN 1.7 section (differences with ICAO):

In the UK, OSGM02 is the geoid model used for determining heights
above MSL.
Parameters for height transformation between OSGM02 and
EGM-96 are not published.
Geoid undulation of the geometric centre of
TLOF or of each threshold of FATO not published.

or for India, GEN 1.7:

The WSG-84 geoid undulation is not published

From a pilot point of view, GNSS altitudes are not used in flight, navigation is based on barometric levels (QNE) or barometric altitudes (QNH). For France, the example in the question, the AIP includes this warning:

GEN 2.1.4.2: User’s attention is drawn towards that publication
of the geoid undulation does not modify the GPS restrictions for use.
Particularly, the altitude information given by GPS has not to be
used.

MSL vs geoid height vs GPS/ellipsoid height
MSL is by definition the height (or altitude) above mean tidal height. The reference has been determined using tidal gauges until recently. Since WGS-84 has been established as the global reference for aeronautical charts (1998), the MSL is approximated by the geoid surface. The height above the geoid is named orthometric height, and referred to as H.

Ellipsoid and geoid, source: Trimble
MSL and H are nearly equivalent, still the definition of the geoid refers to the equipotential of gravity coinciding with the shape the ocean surface would take under the influence of the gravity and rotation of Earth alone, if other influences such as winds and tides were absent. The actual mean sea level can be influenced by local events (like currents) taken into account by a tidal gauge, while the geoid is a surface of equal gravity.
On the other hand, WGS-84 ellipsoid is the approximation of Earth volume as perfect oblate sphere of radius 6378x6357 km. It also tries to coincide with sea level over the globe. The height above the ellipsoid is known as ellipsoidal height, height above ellipsoid (HAE) or h.
While the ellipsoid is a geometric model, the geoid is a physical (gravity) model. With no surprise the ellipsoid and the geoid don't coincide. The geoid can be locally above (up to +86m) or below (down to -107m) the ellipsoid, depending on the local gravity anomalies (mountains, oceanic trenches, crust density, etc). The difference is referred to as the geoid undulation (or geoid height) N.
Of course H = h - N, a vector form, as the geoid and the ellipsoid are generally not locally parallel.
GNSS receivers are able to determine h, any value of H is computed from h and a value of N interpolated from points in a built-in grid established from a gravitational model, ICAO recommends EGM-96 as the global gravity model, but older GNSS use NATO STANAG 4294 Appendix 6.
The way the altitude is computed is:

GNSS determines a 3D position from satellites, expressed as x,y,z in a Cartesian Earth centered frame.
The position is converted into latitude, longitude and h using the ellipsoid model and a polar frame.
Optionally H is computed from h using the geoid model.

Wording used in aviation for GNSS altitudes
The wording related to heights is abused enough in the geodetic field. In the aviation/GNSS field, there is often a specific wording to prevent further confusion:

HAE (height above ellipsoid) should be used for h.
HAG (height above geoid) should be used for H.

and GNSS MSL altitude is sometimes also referred to as Height-Above-Geoid (HAG) (EASA)! Both heights are also qualified geometric, in the sense they are actual distances, not a pressure differences.
GNSS altimetry is not directly shown to the crew (as noted Cody P some avionics may have an option to display them), but appears in automatic processing, like in LPV approaches and ADS-B messages, or in TAWS (as noted by Cody P).
Designing a SBAS approach requires knowing the geoid undulation information
Approaches were the vertical guidance is based on GNSS work with a satellite based augmentation system (SBAS) (well known are WAAS in the US and EGNOS in Europe, but there are other, including MSAS, GAGAN, SDCM, SNAS, see this map), or a GBAS/LAAS. The final approach segment of the procedure is described in ARINC-424 by a FAS data block embedding altitude as HAE, e.g. to describe the landing reference point (LTP/FTP).
However these values are used only by the flight management system (FMS, FMGS) which computes the GNSS approach path. The crew still works with the barometric/radioaltimeter indications to assess minimums and take decisions and the approach is monitored using the standard ILS course deviation indicator.
As the procedure and the aircraft sensors use only HAE values, there is not need to convert them into HAG, the geoid undulation is not required for the process to work. However the procedure designers will likely start with MSL altitudes, and convert them into HAE heights as required, using the undulation information.
The use of GNSS in aviation is still in its infancy, maturity will likely come with future ATS/ATM models and the integration at forced march of the growing unmanned traffic. Whether the geoid or ellipsoidal height, or both will be used is still to define, but...
ADS-B is going to use the GNSS ellipsoidal height
Mode S ADS-B messages contain the barometric altitude (1013.2 hPa) as in mode C and optionally a GNSS altitude which can be based on geoid or ellipsoid height, e.g. for Airbus, it's dependent on the ADS-B transponder standard (DO-260):

A320 and A330

DO-260: MSL
DO-260A HAE or if not available MSL
DO-260B: HAE

A350 and A380: Always HAE

Regulation needs to better define how altitudes will be measured, FAA tries to move forward in AC 20-165B:

Geometric altitude for ADS-B purposes is the height above the WGS-84
ellipsoid (HAE). Geometric altitude is required to be transmitted by
14 CFR 91.227

The choice for h (HAE) is motivated by the fact h is the raw value computed by a GNSS receiver, while H requires an additional built-in lookup-table.
As ADS-B is going to use only HAE, the published undulation information is also useless in this application.

Fantastic answer, although I have two things to add to the "wording" section.  First, there is actually an FAA Advisory Circular, AC 20-163, dedicating to naming orthometric height, which recommends it be kept from confusion with barometric MSL and kept short, with a suggestion of "GSL".  Second, some pages on some devices do display HAG/GSL.  See the Garmin 750 for example.

@CodyP: Thanks for the comment, interesting points, useful additions. I didn't know TAWS was using the GPS altitude, as ACAS uses QNE, but that makes sense.

As a pilot, everything is referenced to the altimeter, or the radio altimeter below 200 feet AGL. It is understood that “GPS Altitude” is somewhat close but won’t exactly match up, but that’s as far as we care.
For military pilots doing targeteering (on the ground, pre-mission), they may well get fairly deep into this sort of thing, but in the airline world, it’s all & only about your altimeter in the panel in front of you.

Is 821 ft ARP altitude determined with a barometer?

@mins most likely surveyed and referenced from a specific vertical datum.

As already explained, in aircraft equipped for IFR, GPS height is not displayed. It is used in EGPWS, but whether that has the map coded with geoid heights and a separate geoid model, or whether it has the map coded directly in ellipsoid elevations is implementation detail of the EGPWS.
However, ultralights may not be equipped with standard instruments and many pilots complement what little they have with GPS units. These are often simple hand-held outdoor units that may not have geoid model in them and thus may show ellipsoid height instead of geoid height (= altitude above sea level).
So my educated guess is that the geoid undulation is published for the benefit of ultralight (including paraglider; also balloon etc.) pilots flying with GPS.

Those who are saying 'everything in aviation is referenced only to the altimeter' are oversimplifying the situation today with GNSS based instrument approaches providing vertical guidance. A barometric altitude will be used to determine the point at which the pilot must go-around if runway environment isn't visible, but the glideslope that the aircraft follows will be generated by a GNSS navigation system onboard using a Geiod undulation corrected 'zero height' datum at the touchdown point on the runway.
It's well known that there will often be differences between the specified check altitude at a certain point on the descent path and the actual barometric altitude, which is why such approaches may specify a minimum temperature below which the approach can not be used.

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text:
Is it possible to reduce the angle of fully extended flaps of an aircraft without affecting lift generated?
I think flaps are inspired from eagle feathers which increase the overall wing surface area and help provide the necessary lift at lower speeds. However, fully extended flaps hang lower and cause more fuel to be burnt (might be because they interact and reduce the exhaust thrust and create more drag). Are the current wing flaps fully optimized or is there any possibility of improvement?
Lowering fuel consumption while maintaining same lift and safety of aircraft by possible geometrical modification is good, because it helps reduce the carbon emissions.

You can rest assured that current flap configurations used in modern aircraft are fully optimized.
Developing new aircraft, and operating them is a multi billion dollar enterprize, and although it would be foolish to claim that design choises are not compromises to some extent, it is certain that no stone is left unturned when aerodynamics of the wing is being designed.
Current solutions are the best that can be achieved with present day materials and budget, not to forget the reliability of the solution.
There are known solutions such as blown flaps, boundary layer suction and so on and so forth, but they all have downsides that make them not utilizable in large scales.
To adress the point of fuel consumption: the current flap configurations are designed to maximize fuel efficiency. Flaps are being used in portions of flight that last for relatively short periods (say, 15 minutes max. for intermediate flap settings, a couple of minutes for full flaps). By utilizing high lift and thus high drag flaps for landing, the wing can otherwise be designed to be very, very efficient for the main part of the flight.

is it possible to reduce the angle of fully extended flaps

Yes.  Fully extended flaps are only used for landing.  They allow for a lower landing speeds and more drag, resulting in a shorter roll-out.
For less drag, they can be reduced, or with higher speeds, fully retracted.
With aircraft, lift increases with the square of speed, which is why flaps are generally used only when the aircraft is flying at a slower speed.
Best distance per unit fuel burned is near the lowest drag configuration.
Weight is critical too.  The best bet for fuel efficiency is to have one wing that is properly sized for the weight and speed desired.
Adding flaps is essentially adding another wing for slower flight.  It works, just not (aerodynamicly) as well.

I’m curious, why did you omit and not answer “without affecting the lift generated?” Did you think this part was irrelevant?  Because it’s really the central point of the whole question.

Might be because the idea that flaps "affect... the lift generated" is the wrong way to think about them. Many factors go into the generation of Lift. Changing the lift is not the point of flaps. The point is to lower the minimum speed at which wing can still generate sufficient lift to maintain 1 G flight.  In actuality, deploying flaps lowers the maximum available lift at most (cruise and higher) airspeeds because it lowers the wings maximum allowable structural load limit.

Good points.  Going by the flaps 0, 10, 20, 30 degrees, 10 increases lift coefficient, 20 and especially 30 mainly add drag.  With flaps, the rest of the wing has to stay lower AoA to keep the flaps portion from stalling (what Charles pointed out).  When airliners drop full flaps, they have Snoopy, the Red Baron, and the whole Flying Circus going on back there.

@CharlesBretana "The point is to lower the minimum speed at which wing can still generate sufficient lift to maintain 1 G flight." And the flaps do this by... (sheepishly from the back row) "by changing the lift sir?" "NO!" (sharp smacking sound...)

@CharlesBretana - re "Changing the lift is not the point of flaps." - but changing the lift coefficient is.  Re "In actuality, deploying flaps lowers the maximum available lift at most (cruise and higher) airspeeds because it lowers the wings maximum allowable structural load limit." - seems odd, as the flaps would appear to cause the inboard portions of the wings to generate most of the lift, reducing bending loads.  Do you have a source for this?  Maybe should be a new ASE question--

Re "With flaps, the rest of the wing has to stay lower AoA to keep the flaps portion from stalling (what Charles pointed out). " - are you sure?  I can understand a claim that the AoA of wing as whole must decrease when flaps are deployed to keep the  net lift force constant at 1 G, but this is different from a claim that deploying flaps while holding AoA of unflapped portions of wing constant will create a stall.

@quietFlyer, yes, almost every aircraft I have flown has had a lower structural limit when flaps were down than when the wing was clean. In the F-4, as I recall, the structural limit was 8.5 Gs clean (up to 37,500 lbs), but with flaps out it was only 4Gs . In Cessna 340 it was 3.8 vs 2.0. Cessna 172, 3.8 vs 3.0, I could go on & on. Why?, because flaps are not built sturdy enough to handle the load they would need to manage at those higher g-loads. They are for flying Slow, during approach and landing. If you extended flaps at maneuvering speed, and tried to turn hard, the flaps would rip off

Secondly, to the comment about lift coefficient, it is not the increase in the lift coefficient that is important, it is the shifting of the lift coefficient curve to the left (to a lower airspeed range), that is the point. This shift allows the aircraft to maintain 1 G flight (at or near the maximum lift coefficient), at a lower airspeed.  THAT is the point.

(Somehow "lift coefficient" is a combination of a particular airfoil and AoA.  So for a given speed, adding more camber allows for lower AoA to generate 1G or allows the same Aoa for a lower speed.  Slats add camber too).  More preaching to the choir.  Ha!

@Robert, My comment about extending flaps at cruise was made simply to explain why flaps are not designed to withstand the forces they would experience then ... i.e. why the design load factor is lower with flaps extended than it is when they are retracted.

But the shifting of the lift coefficient curve to the left, (to a lower airspeed range), is EXACTLY the point of flaps. It most certainly IS a "good idea" to land at the slowest possible safe airspeed that you can. That is the same thing as the "at or near the maximum safe lift coefficient". And shifting the lift coefficient curve to the left is what allows an aircraft to land at lower speeds. Am I contradicting you? I'm not entirely sure if your comment is intended to agree or disagree with my earlier statement, which I entered in response to @Michael Hall, not to your correct answer.

@CharlesBretana thanks for clearing that all up.

Sorry for the confusion!

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text:
Does aircraft nacelle length/shape/geometry affect the contrail formation?
This is coming from Question 1 and further down Question 2.
I think the nacelle and exhaust cone do affect the contrail formation in some way, what is the relationship between them? Do the famous 787 Chevrons also affect the contrails? And How does it  compare with engines with exhaust mixer?

Ultimately the engine is dumping water into the atmosphere and this will quickly cool to ambient temperature.  Depending on the relative humidity at altitude it may or may not condense.  These factors are irrespective of the engine design provided that combustion is more or less complete, so the only factor that will significantly affect contrail formation is the extent to which the exhaust gases are distributed.  This will certainly be affected by the design but is hard to predict in general how; it’s mostly down to fluid dynamics well downstream of the engine itself.

Interestingly, piston engines can also make contrails.  Fans could be mentioned as a factor "to which exhaust gasses are distributed".  A contrail is essentially a cloud, and their (longer lasting) ice crystals must form before the water in the exhaust stream evaporates.  Very cold temperatures with higher relative humidity favor contrail formation.

For whatever it's worth, B-2 bombers often leave very distinctive contrails that can be recognized at a glance.  I can't quite remember exactly what it is about them that catches the eye, but they are distinctive.  Of course, in 4-engine airliners like 747 the contrails become entrained in the wingtip vortices in a way that never happens with other aircraft--

@quiet flyer given the variety of different engine designs in use, I’d say that since only a handful of aircraft have visibly different contrails that’s empirical evidence that engine design such as chevrons doesn’t make a significant difference.


text:
How do flights fly on some special days when there are firecrackers bursting near the source/destination airport?
I mean there might be festive nights like New Year eve, when there is spectacular display of colorful firecrackers in the sky, but when there are flights descending or ascending near a city with an altitude of 3000 feet, I feel that it is risky enough to fly flights that low.

This may be a dupe of this question or this one?

Typical fireworks simply don't go that high. The world record for the highest firework ever is 3,700 feet. Most fireworks only reach 200-500 feet before exploding. The very biggest commercially available fireworks may be able to reach 1,000 feet.
Firework displays are basically treated like cranes or any other obstacle that might be erected in the vicinity of an airport. A NOTAM will be issued, and pilots will know not to fly near the display. Not to mention that they're pretty easy to see, given how bright the typical firework is. But it rarely matters, since the only time a typical plane will be flying that low is if it's just about to land or had just taken off.

Good answer.  I might just add that displays aren't generally planned in the immediate vicinity of airports, and at night they are super easy to see and avoid.

@MichaelHall Good point, I think I'll add it to the answer.

Not too long after I got my PPL, I thought it'd be cool to watch a 4th of July fireworks show from the air. We were somewhere around 1500-2000 AGL and maybe 3 nautical miles away (outside the NOTAM'd area). We were tremendously disappointed. Even from that relatively low height (and we didn't want to go lower at night) the fireworks were tiny little things, way way below us. They just looked like tiny little sparks. The gas money could've been much better spent!

@MichaelHall My home airport hosts a fireworks show every year. It used to be directly adjacent to the field (under downwind leg), but now they close the airport and launch everything from the runway itself :-(


text:
How do I find the historical arrival procedure GOLDN6 for SJC that is no longer valid?
I don’t know exactly when this procedure disappeared.  It was used in 2013, but not sure how much longer.  It was used primarily by SEA to SJC flights.

Welcome to Av.SE.

And, to pre-empt objections about "resource location is off-topic," the real question here is about a method: how to go about researching retired procedures. And that's a perfectly valid question - because the answer isn't to go buy them from Amazon or from Sporty's or from Wal Mart or etc.

No idea how well it'd actually work, but I wonder if an old flight simulator with an "out-dated" database might have some useful info. It wouldn't be the whole plate, but you may be able to get fixes/coordinates out of it.

Understand that the numeric part of the arrival (6 in GOLDN6, for example) changes over time. Maybe the FAA adds, or removes, or changes a speed restriction at a given waypoint on the arrival. The number will go up, and the new version will be effective on a given date. Then in some number of months, something else changes, and the number increments again. When it gets to 9, the next revision goes back to 1.  (Which is okay, since the last GOLDN1 was now years in the past, and what's important is differentiating the current procedure from one that was recently superseded.)
Typically, these revisions are pretty minor, and when airspace gets revised on a large scale, the old procedure names are all retired, and all new procedures are published with all new names.
All of that to say, if you search for "GOLDN arrival SJC" (and don't let the search engine helpfully substitute 'golden' in the query), you may find a chart of the GOLDN4 or GOLDN5, which would most likely be quite similar to the one you're interested in.
I imagine that the FAA TERPS office keeps archival copies of everything that they've ever published, as (probably) would OAK Center and the NORCAL TRACON, and (almost certainly) Jeppesen, but those avenues start becoming a lengthy research project, trying to get in touch with the right person in the right office.
Hopefully this helps with the search.

Turns out that "GOLDN arrival SJC" is less useful than "Golden Gate arrival SJC" -  the first result for the latter is: https://www.fly.faa.gov/Information/west/zoa/sfo/atcCharts/SFO_STAR_00375GOLDENGATE.pdf

I am interested in revisions of GOLDN.  GOLDN6 was the last version.  I did google it and found only one link on flightaware.com to a flight about 8 years ago.  Unfortunately, corresponding  decode page was unable to display the waypoints and lat, long.  So if anyone has ideas on how to find this history it would be appreciated.  Is there a way to search archived NOTAMs?  I would appreciate very specific instructions.  Here is the one flight I found https://flightaware.com/live/flight/ASA324/history/20130718/1925ZZ/KSEA/KSJC.

If this is for research of some kind, Oakland ARTCC (located in Fremont) would probably have the answer in their Airspace and Procedures office. The A&S office keeps current procedures, but should also have access to archive data. Their main switchboard is at 510-745-3000.

The GOLDN standard terminal arrival route (STAR) was decommissioned about a year ago (I write ATC simulations for Denver ARTCC, and have to be current on stuff like this). It had transitions from the east over OAL VOR (in addition to transitions from SEA and others), and we saw it a lot here in Denver. VOR-based STARs are going the way of the dodo, however. RNAV STARs are the future.

Googling does little good if the sought after document is deleted from databases, as in the case of approach plates, and procedure documents like SIDs & STARs is done, for obvious reasons. And anyway, I'd strongly advice against "google it" -answers, as they simply are not usefull at all.

@Jpe61  There is more in the answer than simply "google it," but if that being included is worth the dv, be my guest. See also first comment, above.

Fair enough, I edited the answer to bring the usefull part to the front. Took the liberty to completely remove the obvious.


text:
Lift Pressure Distribution

If the pressure goes always from high to low, we should have a compression, due the lower pressure of the air stream over the upper surface, and an expansion in the airstream in the lower surface.

So What causes the "suction" on the upper surface of an airfoil and the "pushing" in the lower one?

I undestand why there is a region of high pressure and a low pressure around the airfoil. But I am a little bit confused about the effects of the external pressure (Free stream) on the airfoil stream.

Welcome to aviation.SE! We have a lot of questions on this site about lift. This one and this one might be helpful places to start (and check the related questions list for each of them). If those don't help then maybe you could add some more detail to your question about what you find confusing?

Lift is not just about suction and pushing. Thats just a VERY simplified way of explaining to laymen how lift works. A good place to start to get an idea of some of the mechanism involved is here: https://www.youtube.com/watch?v=PF22LM8AbII

The key to the lift generation is the curvature of the streamlines. Forget the popular, but unfortunately wrong explanations based on the non-equidistant particle paths.
The simplest example will be if you place a plate with an angle of attack in the subsonic flow: the streamlines will get curved on the both plate sides as the flow turns.
Therefore, even a flat plate will generate a lift once its angle of attack is different from zero. As the streamlines are turning on the upper surface, the pressure will get reduced from the free-stream to the airfoil surface.
In other words, moving away from the airfoil, the pressure will increase - in the direction of the radius of curvature of the streamlines.
Important to note is, that this pressure drop is normal to the streamlines. This change in pressure is simply an effect of turning the flow, i.e. changing its direction.
Mathematically, the pressure gradient normal to the streamline, dp/dn, can be expressed as
$$ \frac{dp}{dn} = \rho \times \frac{V^2}{R} , $$
where R is the radius of curvature the streamline. Derivation of this equation can be obtained if writing the momentum equations in the natural coordinates.

Would you mind to explain the symbols in your equation? That will certainly make it easier to understand. Otherwise a fine answer. +1

I’m not sure where to pitch this but I’ll have a go...  There are a few ways to look at it - perhaps simplest is that the top surface is longer the an the straight-line distance across the chord and so the airflow must speed up as it is effectively stretched.  If the air were stationary then the surrounding air would move in to equalise the pressure, but it’s a dynamic situation and so the surrounding air will accelerate inwards and so much of the pressure differential remains.

Sounds like a classic "equal transit time fallacy" to me. The bottom of the wing also has a longer than straight chord line distance.

True, for an undercambered wing it’s useful to consider the acceleration of the air as it moves downward to follow the surfaces of the wing.  Still, the notion holds that the surrounding air takes time to accelerate in to equalise pressure and so this only works because it’s a dynamic situation.


text:
What is the distance unit on a navigation display?
I want to learn what is the distance unit on a navigation display.

I pointed the distance marks with red circles on the navigation display. What are these 10, 15 etc. values' unit? Are they representing mile, nautical mile or kilometer?
And can it be adjusted in a different measurement unit (mile, kilometer or nautical mile) or is it a standard unit for aviation and navigation displays?

At top right of the image it indicates that the SBG waypoint is 7.5NM away, and that waypoint is shown exactly (?) between the 5 and 10 range rings on the main part of the display. So by inspection, it's in nautical miles. You can read about standard units in aviation in this question.

They are nautical miles, which is the standard for essentially all discussions of distance in aviation. (Visibility being an exception; it can be reported in essentially every unit except nautical miles.) The software certainly could switch the display to another scale such as kilometers, although I’m not familiar with any systems that provide that option.

In addition the mode (here "arc") and the range (here "20" NM) can be selected using the EFIS control panel.


text:
Is An Electric Plane Possible?
I know we have electric cars already. But in the future we’ll eventually have to use something cleaner than gasoline and gasoline is running out! So is it possible to have a battery powered turbofan plane?

Welcome to aviation.SE! We have many questions about this subject already; this one in particular might be useful for you. It's a very broad topic, so I suggest you look over the questions we already have and see if you can make your question more specific. If you aren't familiar with how the site works, you might also like to take the [tour].

Strictly no, because a battery-powered turbofan is a contradiction in terms (like an electric-powered internal combustion engine).  But yes, there are flyable electric planes that exist today.  Google will return ~5 million hits.


text:
What pose is best for to assume before hitting the ground for survival after failed parachute?
The title says it all. Assuming one is falling down on a hard perpendicular surface after reaching terminal velocity, what pose provides the highest chances of survival?
My guess would be one of the poses on the picture below (sorry for crude sketch, notice the back is curved):

The rationale behind both is that a lot of energy gets dispersed through the limbs, which are the least vital part of the human body, and the general shape is a slight curve so that the victim rolls over as shown by the arrow, dissipating energy consequently up to his head. I'm not sure which of the two is better: the first one provides a little more protection for the head, but the right one can probably help save more vital organs in the torso in the same way legs do.
How liable is that?

Head first, then I don't have to deal with being paralyzed, massive hospital stays, rehabilitation, and life-long pain, not to mention the bills and inability to work.

@RonBeyer Not like you couldn't write books about how you survived the fall even paralyzed. Bet that'd sell

Maybe, but look at the "famous fall survivors", don't think any of them died rich. My life insurance will probably pay more than a book deal. Another plus is if I get going fast enough they won't even have to bury me, I'll take care of that on the way down.

I believe the best "position" is straight up/down, feet first. You will break every bone in your body up to your back, but the goal is to keep your head from slamming down. The two positions you show will result in your head hitting the ground basically at the same speed. You also want to avoid your chest from slamming down (lots of important things in there along with pointy/fragile ribs).

Before we discard this, let's remember that few parachute failures are total failures (even among the tiny number that aren't dealt with by a reserve chute).

Grab your legs, bend over, and kiss your butt goodbye. Impacting at terminal velocity, your arteries will rupture and you'll bleed out, even if your skull isn't fractured.


text:
Why does increasing thrust on one engine make the plane roll and not yaw?
If you increase the thrust on the right engine, the plane rolls to the left. But why? And why does the plane roll to the right and not yaw to the right?
Note: I am not a pilot, nor have I followed any aerodynamic studies whatsoever.

Increasing thrust on the right engine only will make the aircraft yaw and then roll to the left.
The thrust does generate a yawing moment to the left, but the secondary effect of yaw is roll. In simplistic terms, a yaw to the left means that the right wing not only momentarily moves through the air faster than the left, but more of the wing is exposed to the airflow. This generates extra lift from the right, putting the aircraft into a left roll.
A more technical explanation of this effect can be found here.

The selected answer on the linked physics SE presumes that the sweep angle is the main factor in the yaw/roll coupling. This is incorrect. In reality, the dihedral angle is the most significant factor. (The rule of thumb is that 1° of dihedral is worth about 10° of sweep). But the main point is, right, that the roll is only a secondary effect; yaw (or more correctly, sideslip) must happen first. The whole question arises perhaps because roll is more immediately noticeable than yaw.


text:
How to deduce the dynamic general equations for a non-symmetric level turn manoeuvre?
I'm currently studying flight mechanics on a subject at my engineering degree and I'm trying to solve some standard case exercises with the general equations and diferent reference frames.
I've been able to solve multiple exercises on different looping manoeuvres enclosed in the vertical plane but I can't deduce the general equations for a horizontal plane.
$$ T
\cos\varepsilon\cos\nu - D - mg\sin\gamma-m\dot{V}=0\\
T\cos\epsilon\sin\nu-Q+mg\cos\gamma\sin\mu+mV(\dot{\gamma}\sin\mu-\dot\chi\cos\gamma\cos\mu)=0\\
-T\sin\varepsilon-L+mg\cos\gamma\cos\mu+mV(\dot\gamma\cos\mu+\dot\chi\cos\gamma\sin\mu)=0
$$
So starting with the above and taking into account some simplifications I get to an intermediate state which is quite similar to the solution for the problem which is the following:
$$T\cos\nu-D=0\\
L\sin\mu+T\sin\nu\cos\mu=\dfrac{W}{g}\dfrac{V^2}{R} \\
L\cos\mu-T\sin\nu\sin\mu-W=0$$
My question is: How is it possible that the Lift term appears in the second equation if the starting equation didn't consider it? And also, why the trigonometric relations for the thrust change?
(This results are for a non-symmetric manoeuvre).
I can't get in my mind why the general equations used in all the books can't give in a direct way the desired result without adding new terms.

Reference frame for the equations is wind-axis.
The angles used are:
$\nu =$ Thrust side-slip angle
$\varepsilon=$ Thrust angle of atack
As we are using wind-aixis reference frame:
$\mu=$ velocity roll angle
$\gamma=$ velocity pitching angle
$\chi=$  velocity yaw angle
$W=mg$, $T=$ thrust,  $D=$ drag, and $Q=$ lateral aerodynamic forces

Your angular notations are different from the western industry-standard. You should explain first what these angles refer to. And what do you mean by non-symmetric turn?

I've edited the post with the references for the angles. The non-symmetric turn means (from what I understood from my books) that the forces on the two wings are not balanced basically the lift, also, the thrust side-slip angle is different from 0.

I edited your equations to MathJax. Please check if I made any mistakes in transcribing your equations. Remember to use \cos and \sin rather than plain cos and sin, so it is typeset as a function rather than plain variables.

Checked! Now everything is correct. :)

Your equations seem to be in wind-axis, and look a little weird from my literature (referencing Stevens and Lewis, Aircraft Control and Simulation). I'm more used to specifying mechanics from the body-axis.
Legend: $\theta$ is Euler pitch angle, $\phi$ is bank angle, $\psi$ is yaw angle, $p$ is body roll rate, $q$ is body pitch rate, $r$ is body yaw rate, $\alpha$ is angle of attack, $Y$ is aerodynamic side force (in stability-axis), $u$ is body forward speed, $v$ is body lateral speed, $w$ is body vertical speed.
A. Thrust aligned with body-axis
I will assume:

Thrust is aligned with the body-axis.
All aerodynamic forces are aligned with the stability-axis (see this question for the rationale).
No wind, so that the velocity in body-axis is the relative air velocity ($\alpha=\tan^{-1}(w/u)$,$\beta=\sin^{-1}(v/\sqrt{u^2+v^2+w^2})=\sin^{-1}(v/V)$).

For the general 6-dof, we have:
$$T-D\cos\alpha+L\sin\alpha-mg\sin\theta=m(\dot{u}+qw-rv)$$
$$Y+mg\cos\theta\sin\phi=m(\dot{v}+ru-pw)$$
$$D\sin\alpha-L\cos\alpha+mg\cos\theta\cos\phi=m(\dot{w}+pv-qu)$$
In a coordinated turn, the ball is centered, which means that the gravity component cancels out the centripetal force, and the aerodynamic forces in the y-axis must be zero.
Furthermore, in the inertial frame, we should only see a non-zero yaw rate ($\dot{\psi}$) for a steady turn. So translating this back into body-axis, we have:
$$p=-\dot{\psi}\sin\theta$$
$$q=\dot{\psi}\cos\theta\sin\phi$$
$$r=\dot{\psi}\cos\theta\cos\phi$$
To make the matter somewhat clearer, we can choose to make small angle assumptions on $\alpha$ and $\theta$, and $u\approx V$, and eliminate all second order terms. This brings us to:
$$T-D+L\alpha-mg\theta=m(\alpha V\dot{\psi}\sin\phi- \beta V\dot{\psi}\cos\phi)$$
$$mg\sin\phi=mV\dot{\psi}\cos\phi$$
$$-L+mg\cos\phi=-mV\dot{\psi}\sin\phi$$
From geometry, a particle tracing out a constant circular path with a rate of $\dot{\psi}$ will have a radius (i.e. turn radius) of: $R=V/\dot{\psi}$. So the second equation is now:
$$tan\phi=\frac{V\dot{\psi}}{g}=\frac{V^2}{gR}$$
We can define a stability-axis load factor ($n_{z_s}=\frac{L}{mg}$), which would closely approximate the body load factor for small AOA. The third equation can be expressed as:
$$n_{z_s}=\cos\phi+\frac{V\dot{\psi}}{g}\sin\phi=\sec\phi$$
At this point, we've completely reproduced the performance equations relating load factor, bank angle and turn radius from the 6-dof equations.
B. Thrust asymmetric with body axis
Let's say that the thrust vector is angled with the body axis by a pitching angle of $\epsilon$ and a yaw angle of $\nu$.
So in the body-axis, the thrust vector is:
$$\boldsymbol{T_b}=\begin{bmatrix} \cos\epsilon\cos\nu & -\cos\epsilon\sin\nu & \sin\epsilon \\
\sin\nu & \cos\nu & 0 \\
-\sin\epsilon\cos\nu & \sin\epsilon\sin\nu & \cos\epsilon \end{bmatrix}
\begin{bmatrix}T \\ 0 \\ 0 \end{bmatrix}$$
We now have modified 6-dof:
$$T\cos\epsilon\cos\nu-D\cos\alpha+L\sin\alpha-mg\sin\theta=m(\dot{u}+qw-rv)$$
$$T\sin\nu + Y+mg\cos\theta\sin\phi=m(\dot{v}+ru-pw)$$
$$-T\sin\epsilon\cos\nu + D\sin\alpha-L\cos\alpha+mg\cos\theta\cos\phi=m(\dot{w}+pv-qu)$$
Again assume that the ball is centered, thus $T\sin\nu = -Y$. The conclusion from the second equation (relating bank angle to yaw rate and turn radius) would be the same as before.
The third equation can be reduced to:
$$\frac{1}{mg}(T\sin\epsilon\cos\nu+L)=\sec\phi$$

Thanks for your elaborated answer, I really appreciate it. But, still, I see what you are doing with this on the body-axis, as getting back to my initial question you have from start on the x-axis equation the terms for Thrust, Drag and Lift, and the same for the z-axis (Lift, Drag). In my case when starting with the equations referenced in (3.5) lift doesn't appear in the y-axis but it's in the answer for the exercise. I can imagine that, while in the turn and with the plane in a banking angle its normal that some of the lift is also produced in the Y axis from a wind-fram point of view.

But I don't know how to incorporate it to the wind-axis equations and what is the procedure to get there and solve it using the wind-axis. Thank you again for taking the time to answer.

@RogerVallès Sorry, I prefer the body-axis :) See my modified answer and see if it helps any.

Yes, with the new part that you added I've been able to deduce what I was missing. I draw the thrust and the lift vectors on the Fh plane and then moved them to the wind-axis with the transformation matrix and got the final result. I've been thinking about it for a while and it looks more logical to use the body-axis for most of the calculations, but I'm not in a position to choice what axis to use as that's what's on my book for the subject and all the exercises are usually with wind-axis. Basically I think my teacher likes the wind-axis a lot more hahaha


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Are tower simulators used in civil ATC training?
Pilots use cockpit simulators, what about training  of air traffic controllers working in control towers?

Control tower of Québec / Jean Lesage airport (CYQB). Source.
How do they train? Are there full visual simulators with runways, taxiways, radio traffic, etc?
The question is valid for a country with large aerodromes.

I'm pretty sure I have seen photos/videos of one with giant flatscreens (or maybe they were back-projected movie screens) as windows, so that would be a "Yes" for a fully VR simulation, including windows.

http://www.airtrafficmanagement.net/2012/07/airways-nz-installs-sa-total-control-360-sim/

O'Hare (KORD) has a very realistic 315° simulator in one of the towers. They even have VR simulations for rescue/fire equipment.

You should have visited the World ATM Congress (last day was today). There were many impressive ATC simulators, including for tower training.

@DeltaLima: I wish I worked in this business.

@RonBeyer Not to be confused with "Airport Firefighter Simulator 2013" which is apparently a game.

aka Flughafenfeuerwehr Simulator 2013

@Michael Yes, but honestly a lot of companies that manufacture the "real world" simulators also have game type ones as well to prop up development costs. For example, VStep Simulation has a highly realistic vessel simulation package that I've used to prove out ship control systems. They also sell a game version.

@RonBeyer Ah, that's good to know... perhaps that explains the proliferation of apparent games such as "forklift simulator" which might strain one to wonder the appeal of.

I can see forklift simulator being fun and educational, however this one I'm still trying to figure out.

On the non-professional side, there is also VATSIM.

Absolutely (and not just civil ATC training - military as well). A large part of modern ATC training is simulator training. This is true for all types of ATC - area control, approach and aerodrome (tower).
For area and approach, the simulator is fairly simple, since the essential bit is a radar screen and a screen with flight information. For tower, there is the visual aspect as well, which makes tower simulators quite large and complex. Some tower sims are relatively simple - 4 big TV-screens with a 3D model of the airport, and a couple of computer screens with radar and other equipment. There are also full size, 360 degree sims, where the "windows" are created by an array of projectors or large screens. After working traffic in one of those for a few minutes, you start to forget that you're not in a real tower.
During simulator training, students can run scenarios in the simulator that are either based on generic airports or real airports. The traffic levels and situations can be tailored to match the expected learning curve of ATC students. This makes simulator training a great tool for both initial and recurrent training of air traffic controllers. Much like pilots, after getting our license, we have to go back to the sim once a year to practise unusual situations, emergencies and so on.
For every controller position in the simulator, there are 2-3 connected "blip driver" positions, from where the aircraft movements are controlled. The controller in the simulator will talk to the blip drivers via "radio", and the blip drivers will respond as pilots and provide the necessary input to make the planes move around accordingly.

Side question: do any training facilities ever hook pilots in flight sims into the same virtual world as the tower sim and make the sim-takers deal with each other?

@StarWeaver yes this happens. I know of at least one ATC / airline combination that does a yearly simulation of an emergency scenario where the simulators of the airline are connected to the ATC simulator.

In fact: yes!
Here in Germany the controller training starts off with much classroom lessons to learn the theoretical basics and only some sessions in the tower- or center simulator. During the training the amount of theoretical lessons decreases and the simulator sessions increase. The last few month consist of simulator sessions only, so it's a huge and important part of the training.
A video about the so called "towsim 3D" can be found here.
And here are some pictures taken by me (click each for higher resolution).

The answer is yes, tower simulators are indeed used in civil ATC training.
An example video of a professional ATC simulator can be seen
here. It shows that not only tower control training is supported, but also ground control (executed from the tower cabin), approach, and area control. The student can be at various skill levels (to become a controller, to refresh current controller license, to transfer to a different working site). It is also used for AFISO training (for Flight Information Service training). Training can be targeted for any purpose: Military operations, VFR traffic, de-icing conditions, emergencies like bird strike, fire situations, and so on and so on.
More in-depth descriptions can also be found at this blog, mainly about the simulator and how it works, but also other areas where an ATC simulator can be used: New airspace design, airport construction work, and more.

Welcome to Aviation.SE! These are nice additions, but they sound more like a comment than an answer. Could you please expand your answer a bit? Also, just linking to a resource is not as good as including the main points here, since the link might become invalid over time. - From Review


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What is this aircraft with pipes at the flight deck windows?
This image comes from a site about aircraft tractors:

What could be the reasons for this old aircraft to have pipes at the flight deck windows and to be moved near a forest?

They might be exhaust for portable air conditioning systems.

I doubt it, it does look like a non-functioning aircraft (a 707 I think), and judging by the attire of the people, in a warm climate. The pilots windows are the most easily removed since they are designed to be opened anyway. In fact, I believe that this is the aircraft in the picture above.

@RonBeyer: Ah this is a really strange story with all the spices for a novel. Thanks for sharing. Would you want to write an answer? I'll change the question into a more general one...

@mins Sure, I will write something in general

This picture poses several questions to this Aerospace fan who has never set foot beyond places passengers are allowed. Farhan below mention that it looked like the aircraft was fitted to an ARTS - but between the center fuselage and the ARTS, what are the blue and white objects? On the port wing there, underneath the ARTS support where is what looks like a hose of a similar color - what is that? The three men in blue shirts look like firefighters to me, could the tubes be exhausts for some kind of "plane on fire" smoke drill?

In most commercial aircraft, the cockpit windows are the most easily opened/removed.

(Image Source)
Why the windows typically open is a topic for another question, but mostly it is for the crew to be able to communicate with the ground personnel and for rapid evacuation.
Some older aircraft like the 707 in the original post are used primarily as training devices. The aircraft in the original post is a Boeing 707 in Germany used for evacuation training. The most likely explanation is that they put in portable air conditioning units to be able to cool the cabin while they filled it with people. The vents are angled down so that water does not enter the air conditioning system.
Specifically regarding the aircraft in the post, this is a Boeing 707 located at the Tegel Airport in Berlin, Germany. It has a lot of history being an aircraft that was hijacked and then later smuggled back into Germany in the night by an American crew as a gift from Boeing to celebrate the city's 750th birthday.
You can read more about the Tegel 707 on this website and some more information about the hijacking of El Al Flight 219.

Your links seem to be describing two distinct hijackings, one in 1969, one in 1970.

I believe the first article has the incorrect date and flight number, the hijacker, Leila Khaled was responsible for hijacking TWA 840.

Wikipedia says Leila Khaled was responsible for two hijackings. Note the different name for the other hijacker in the two hijackings.

Other Google results also indicate her involvement in two hijackings.

Wait, you can smuggle a 707? This opens whole new realms of possibility.

@user2357112 You're right, I changed the link to the correct hijacking for this aircraft.

@Delioth Yes, stickers were placed over the Lufthansa markings on the aircraft and flown in the night to the airport so ATC wouldn't turn the flight around. In the late 80's Lufthansa couldn't fly into West Germany, and neither could German pilots. The Lufthansa livery was covered with white stickers and flown by an American crew to "smuggle" the aircraft into the country with Lufthansa livery.

This should read "attempted hijacking of el al 219". They never managed to.

The aircraft tractor you see is an Aircraft Recovery Transport System (ARTS) developed by Goldhofer:

Image Source
You can read more about Goldhofer's ARTS here and here (PDF).

Do the wing-contacting portions of this bear weight, or just stabilize?

They bear weight, @msouth, you can see the wheels up in the air in the first image.

It seems this doesn't answer the question at all (still the details about the tractor are interesting)


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What's the difference between Free-Flight and Free-Route?
I have been reading documents about the concepts of Free-Flight and Free-Route that are being implemented (or being simulated to be implemented in the future) in Europe since 2012 by the initiative Single European Sky, that aims to provide a safer and more efficient airspace.
I have noticed that the concept is similar but it is treated differently, and I am wondering what's the main difference between these two concepts. Also, is it a safe concept? (It involves more possible conflicts in the airspace, if not carefully implemented).

Do you have any reference to free-flight being implemented? The two are very different, but before I answer I'd like to see what you are referring to for free flight.

@DeltaLima I have read that free-flight is not yet implemented but it is being simulated with TAAM and VAMS (Total Airspace and Airport Modeler / Virtual Airspace Modeling Simulation). However, the Free-Route concept is already implemented in some free-route airspace zones (e.g. Maastricht). I modified my question to clarify that.

The difference is between the definition itself.

Free Flight : Free flight is a developing air traffic control method that uses no centralized control (e.g. air traffic controllers). Instead, parts of airspace are reserved dynamically and automatically in a distributed way using computer communication to ensure the required separation between aircraft. This new system may be implemented into the U.S. air traffic control system in the next decade.[citation needed] Its potential impact on the operations of the national airspace system is disputed, however.

This effectively means that, if a part of space is reserved for free flight, you can effectively do anything with your flight plan. Moreover this reserved space would change dynamically, so if there is an approaching aircraft nearby., your free flight space changes to accommodate free flight space for the other flight as well. Both of the planes would have DIFFERENT free flight space, and they can adjust their flight plan just in their own flight space. This eliminates the need for ATC completely.

Free Route Airspace : Free Route Airspace (FRA) is a specified airspace within which users may freely plan a route between a defined entry point and a defined exit point. Subject to airspace availability, the route can be planned directly from one to the other or via intermediate (published or unpublished) way points, without reference to the ATS route network. Within this airspace, flights remain subject to air traffic control.

Here, the Airspace allotment remains under the control of the ATC, which allocates single space to multiple planes, and there one can decide which path to take. Here, inherently there is a possibility of overlapping routes (Because of the same airspace being allotted to multiple planes), and thats why, some routes are allowed in this space, and some are not.

Moreover, there is the Sectorless ATM Concept of DLR researchers Korn et al.:

Feasibility of a new air traffic management concept is examined which might increase the efficiency of en-route operations by up to 100%. The concept follows the idea of a sector-less airspace organization. Aircraft entering the airspace (e.g. the German airspace or the entire European Airspace) will be assigned to one controller who is in charge of controlling the aircraft from entry point (or TMA exit point) to exit point of the airspace (or TMA entry point). First simple real time simulations revealed very promising results. The concept seems to enable an easy transition into a user preferred trajectory (direct-to) operations whilst at the same time increasing ATCO’s efficiency and airspace capacity.

They found that in their scenario the number of potential conflicts between  trajectories that take the direct path from entry to exit point decreased about 30° relative to potential conflicts between trajectories on the traditional airways.


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Why Airbus A220 if A320 already exists?
Airbus just presented its new A220 aircraft, formerly the "old" Bombardier CSeries, that is re-branded after a 50.01% acquistion of Bombardier by Airbus.
It's an aircraft very similar in target and characteristics to its own A320neo Family, so my question is simple... why? If they would cover different market segments this could be a logical choice but in this case, is there not the risk of creating internal competition?

Minor quibble, but the 50+% acquisition is not of Bombardier but of a subsidiary private holding company that owns the C series physical and intellectual assets Bombardier created to wall off the C program from the rest of Bombardier Aerospace.  Airbus controls that, not the larger BA.

You say "It's an aircraft very similar in target and characteristics", but this is not really true. I made a quick comparison of typical number of passengers and MTOW (based on data from Wikipedia):

You can see that the A220 is significantly smaller and lighter than the A320 and A321, more similar to the now discontinued A318 (and maybe A319).

The A320-318/319 or the improved A320neo-319 share the market area around 107 - 160 passengers with the CSeries (now A220), two main differences are:

The CSeries is designed generally for carrying less passengers than the basic A320-family. The fuselage of the A320-family is stretchted or compressed, exemption is the A320-318, which has also smaller wings, but at some point strechting/compressing the fuselage becomes inefficient.
The CSeries is an entirley new plane, while the A320neo seems to be more some kind of improvment with new engines and some(?) modifications to the airframe.

Basically, the airframe, fuselage and engines should fit together, to make an efficient plane. The CSeries should be therefore more efficient with small numbers of passengers. The A320-318 will be not available as neo and the A320neo-319 seems to be market for special long-distance and hot-and-high (engines produce more thrust and consume more fuel) situations.

There will be A220 stretches to take it directly into competition with the larger products, which are rapidly ageing designs, and that's the thing.
The 320 is 30 years old, and the 737 is a 50+ year old design. Sooner or later airlines are going to want something more up to date and the C is state of the art if slightly more conservative than the 787 (aluminum alloy for the fuse, and they wisely decided to stick with NiCad batteries). If design age wasn't an issue they'd still be building 707s and DC8s.
One key example of the benefit of state of the art design is maintenance. The C's maintenance program requires a fraction of the labour hours of previous generation airliners.
It's too bad. The financial strain of the C was on the verge of bringing the whole company down when Airbus stepped in to take it on for free. The experience has left Bombardier Aerospace quietly backing out of the commercial aircraft industry (it is seeking to offload the turboprop program and RJ production will slowly peter out) and in 5-10 years will be a bizjet only operation.

The age of a design is not as big issue. 707s and DC8s are not used anymore because back then they needed four engines where we can now do more efficiently with just two. The two engine designs didn't change that much since 737 was designed. And military still flies many 707s (C135 and KC135).

So, I dug around and this is what I could find:
Airbus and Boeing both cover mainline (130-240 pax upto 3300 nm) with their A320neo and 737 MAX lines respectively.
For regional travel, which is less than 130 passengers, there is the A220-100 and -300. Airbus now covers this section thanks to their acquisition of a majority stake in the CSeries line from Bombardier. So the new A220 variants don't quite compete with the A320neo (especially since the A319 hasn't been doing so great in terms of sales)
This article explains it in greater detail.
Here is more about the CSeries/A220

Actually the Leehamnews article you linked (which is very interesting BTW) is saying something completely different to your answer: "In the end, the CSeries became more than a step-up regional. The present CSeries transports 100 to 150 passengers on routes of up to 3,300nm. These are flights lasting over seven hours." So the A220 does play in the same league as the A320/B737, just with fewer passengers - perfect for smaller airlines like Air Baltic.


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Is there a standard install direction of the abradable shroud honeycomb on a CF6-80c2 engine?
Is there a standard install direction of the honeycomb cells on the Fan Forward case on the CF6-80C2 abradable shroud section?
I have seen engines that the honeycomb cells run point to point front to back. I have seen engines where the cells run point to point in the direction of the circumference of the the abradable material for the Fan blades. I have searched the manuals and I cannot find where the orientation of the honeycomb is specified.
Any repairs are understandably performed with the same orientation.  I am wondering is there a MFG standard?

As noticed by Daniel Kiracofe, this applies to the turbine, but as far as orientation is concerned the logic is the same
The abradable material in the honeycomb cells can readily withstand the high temperatures encountered in the turbine stages of the engine and protects the annular steel backing from high temperatures as well as providing a smooth gas flow surface. However, under extreme operating temperatures, the turbine blades may expand sufficiently to actually rub the surface of the abradable alloy overfilling the honeycomb material, whereupon the abradable sealant material will yield so that the turbine blades will not be damaged
However, the abradable material filling a given cell of the honeycomb can become loosened and fall out due to thermal cycling, rubbing of the abradable filler against the turbine blades, engine vibrations, or can otherwise be blown out by action of the hot gas flowing across the seal.
The orientation is the one, the manufacturer found the least probabilistically susceptible to allow the abradable material to separate; internally the cells walls are not strictly perpendicular to their outer flat surface, and this angular orientation prevents to the best the falling of the abradable material. Thus indeed, as you write, the repairs are understandably performed with the same orientation, using identical material.

This doesn't really answer the question.  OP is clearly asking about the fan module and this answer discusses turbine module.  Any honeycomb in the turbine module may or may not be oriented the same way as in the fan.

@Daniel Kiracofe, Thank you, I will edit


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How do aerobatic aircraft land?
The aerobatic aircraft I've seen don't have any flaps or air-brakes, besides they're taildraggers so I guess they usually have to do stall landing or three point landing but I don't understand how the pilot controls the approach speed or just how they slow down.

The same as any other powered aircraft would - controlling their descent with a combination of pitch and power.
Most small GA type aircraft don't have air brakes, spoilers etc anyway, so that's fairly immaterial.
I'd imagine almost any civil aircraft can be landed quite safely without flaps - it certainly forms part of the standard training syllabus for the PPL and you'd likely be expected to demonstrate a flapless landing on your skills test. The only difference is a slightly faster approach and more nose high attitude.

The plane slows down from aerodynamic drag. Level off above the runway ( also referred to as the "flare"), and wait - the plane will slow down by itself, as it does the wing creates less left, and the plane will settle down to the runway. Holding the nose up as that happens helps to create drag and slow it down.

You can land all planes without flaps etc..
It's just the question, if it is a landing or an arrival
In crosswind situations, a lot of pilots prefer to do little to none flaps set, as the plane stays more controllable.
Btw. you can slow down the plane by pulling the nose up. Putting the nose down increases the speed.
This helps to adjust the speed.

Just to elaborate for the viewers - it's not that flaps make the plane unstable, but less flaps allows you to more easily increase the approach speed which does make it more stable

@Dan Thanks. That's of course correct.

@David That’s not how I was taught or how I fly. The purpose of flaps is twofold: increase the descent angle and reduce the stall speed. If there are gusty conditions, pilots will increase the approach speed by 10% and not put in the last notch of flaps. This gives them a greater margin over stall speed and less drag (the third notch of flaps mostly adds drag). A sudden gust of wind then wouldn’t inadvertently stall the airplane before the flare.


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Using a standard PC gaming / smartphone headset for passengers in a small plane
There is a very similar question to this, but all answers and discussion pertain to just the PC headphones, and not headsets (the headphones with microphones). Gaming headsets have a boom mic and cable with dual connectors (pink/green), both 3.5mm, one stereo (for headphones), the other mono (for the mic). Standard smartphone headsets have a mic on the cable and a single 3.5mm TRRS (tip-ring-ring-sleeve) combo connector. There are plenty cheap ones with active noise reduction, decent audio quality on both headphones and mics, and more importantly, many people already have them. There are also plenty of Bluetooth headsets (with mics).
A possible solution would be building a Bluetooth adaptor that could plug into the intercom, and then pair with the passenger’s headset to allow them to communicate with others. Bluetooth frequencies are well outside the range of any of the nav/com systems, and even so, they would give the pilot a good excuse to avoid passenger distractions during departure /approach (by turning the Bluetooth transceivers off). Resourceful home builders could easily get the necessary electronics for the Bluetooth transceiver (and adjust the impedance as needed).
If the mic (and headphone) impedances are reasonably close, wouldn’t a simple cable adapter be all that’s needed to enable connection?

Does this answer your question? Can normal PC headsets replace 'aviation' headsets?

Something to note is that an adapter for the prong size would be required to even get the gaming headset to plug into aircraft jacks. Aviation jacks are not 3.5mm. Although, many audio panels have 3.5mm aux jacks for music, they are input only stereo jacks. As far as powering the microphone, the gaming headset would need its own power source for active noise canceling like ANC headsets have. But, whether the normally panel powered microphone set up of an aviation audio panel would work with a self powered mic is doubtful. There would need to be some type of circuitry in the adapter.

The answers to the prior question mainly focus on headphones (without a mic), rather than headsets (that include a mic).
There are many quite cheap noise cancelling headsets with a microphone, with the only possible difference being the lack of noise cancelling on the mic itself. These may be perfect for passengers, if they could be properly be connected to the intercom.
Nobody is making an adapter that will have a female 3.5 mm TRRS connector on one end and two plugs (6.3mm and 5mm, for aviation-standard headphones and mic) on the other end. These couldn't be that expensive to make.

This is an interesting question. But, I don’t see what this solves. There are aviation headsets as cheap as $50. That is as cheap as gaming headsets. But, they are specifically designed for aviation to include passive noise reduction. There would be no advantage to using a gaming headset in aircraft.
The primary purpose of aviation headsets for the pilot is to provide clearer communication between the pilot and ATC. But, that purpose shares equal importance with the goal of hearing protection.
Small, General Aviation aircraft are very loud. But, aircraft have speakers and microphone handsets that make communication with ATC still possible. In decades past, headsets were not even worn in enclosed cabins. And, it has only been recently that the effects of noise has been considered a factor in fatigue. Unless the headset addresses the concern of noise reduction, it is of little benefit in the aircraft.
For passengers, noise reduction can be accomplished with industrial or firearm hearing protection. Non-crew member military personnel function with only standard earplugs aboard aircraft. Communication between personnel in the aircraft even with the doors open is accomplished through shouting over the ambient noise. As far as the pilot turning off a Bluetooth device to enforce “sterile cockpit” practices, that can already be accomplished as a built in function of the aircraft audio panel.
So, although a very simple adapter could be built to enable gaming headsets, cellphone headsets, and earbuds to be used in aircraft, it does not truly solve the problem you posed so far. And, it is not truly better than purpose-built aviation headsets. However, my purpose-built aviation headset is Bluetooth enabled, and can be used with a Bluetooth enabled computer like a gaming headset.

Foam earplugs are very poor in GA airplanes because the dominant noise is 70-90 Hz where foam doesn't don't work well.  You think you're getting a decent noise reduction but your lower frequency hearing is getting hammered.  I use 3M Push-Ins, the little yellow ones with the blue peg, with the shaft wrapped in few inches of lead foil tape, used to ballast golf clubs, then heat shrink tubing shrunk over the tape.  The lead tape provides the required low freq damping, and they are VERY effective.  If I have them on under my headset, I can turn my ANR off and can barely tell the difference.

Thanks @JohnK. Although, it has been decades since I had to use military earplugs, that is good info to know. Now, I use Bose and Lightspeed. For shooting, I use purpose-built earmuffs.

Being cheap, I bought a Headsets Unlimited ANR retrofit kit for the Dave Clarks I've owned since about 1976, but I've been thinking of dropping the cash on one of those newfangled ones.  They seem to perform about the same, but the Lightspeeds seem to be more robust (mostly metal construction).

There are many very cheap noise-cancelling headsets out there that connect with a 3.5mm TRRS (smartphone) connector. This would work quite well for the passengers in the back seats, allowing them to hear the pilot, and if necessary, respond.

The main idea is, people already have these headsets at home. If they can plug them into the intercom (as passengers), I wouldn't need to have extra headsets, for all the passengers.
I wonder if the "helicopter adapter" would actually work (it has the 3.5mm female on one end and the two large male plugs on the other).


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Is engine shp directly correlated with its payload capacity?
For a turboshaft engine, does increasing its shp also increase its payload capacity?
What are the other factors determining the payload capacity of a helicopter?

Without all the appropriate supporting modifications (like transmission, blades, etc) the answer would be no.

This is a complicated question, here is a simplified answer.
Generating lift requires setting in motion a large quantity of air, as downwash. More lift requires more downwash, and that requires setting in motion a larger quantity of air- which requires more horsepower applied to the main rotor shaft.
Note however that the rotor blades are designed to generate their optimum lift at a certain design speed and angle of attack, which means that if you add horsepower you would also have to increase the rotor blade span and/or add more blades to absorb and make best use of the additional power- all while maintaining the blade tips subsonic, and not overstressing the blade attach points or the main transmission gears and shafting.
In addition, more power to the main rotor disc means more torque reaction, and you'd need to redesign the tail rotor to counteract that.
All this means that you cannot increase payload by simply increasing the shp of the engine.


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For a coaxial rotorcraft, Do horizontal and vertical stabilizers in the tail really make much of a difference?
Can we design a coaxial rotorcraft without tail and tail boom completely? What might be the consequences?

The horizontal tail surface is there to generate downforce that holds the nose up in cruise. Without it, the faster you go, the more the nose points down as the machine's body wants to "trail" so to speak behind the tilted rotor disc.
The vertical tails are to provide a weathervaning effect to make the machine passively point ahead in forward flight without requiring a torque control input.
Take those surfaces away, and you are stuck with pointing down at an unpleasant angle while cruising, and having to constantly work the pedals to keep it pointed straight. A fly by wire yaw stabilization system working the pedals in the background could probably take care of the yaw part, but I don't know how you could deal with the pitch part without a stabilizer surface.